Trailer cargo detection using ultrasonic transducers

ABSTRACT

A cargo detector for use in a trailer that includes an ultrasonic transducer for covering the entire interior area of the trailer. In particular, the cargo detector has three modes including short range, long range, and proximity range, and can detect cargoes located flush against a front or rear wall of the trailer.

RELATED APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/400,664, filed Aug. 1, 2002. The entire teachings ofthe above application are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] Mobile asset location tracking systems have been available sincethe 1980s. These systems typically place a locator sensor, such as aGlobal Positioning System (GPS) receiver, and some sort of wireless datacommunicator system, such as a cellular telephone, to periodicallytransmit its location to a central dispatch or controller. Knowing thelocation of trailers has proven to be extremely valuable to traileroperations. Initially, this technology was primarily utilized forexception management, but it has since proven to also be valuable forimproving the efficiency of trailer utilization.

[0003] One key piece of information used in optimizing trailerutilization is to know when and where a trailer was loaded, and when andwhere the trailer was unloaded. Until recently, trailer operationsrelied on the accuracy of reports from drivers for this information, buthistorically, this method of reporting is often inaccurate.

[0004] Object detection techniques utilizing ultrasonic transducers hasalso been available for years, but the application of this invention forcargo detection in a trailer had not been exploited until just recently.Ultrasonic detectors address a key issue in trailer cargo detection inthat the sensor can be mounted in one location, and the detection signaloriginates and returns to that same location. Consequently, theinstallation and cost is manageable.

SUMMARY OF THE INVENTION

[0005] Cargo detection in a trailer is a difficult accomplishment,primarily because of the obtuse dimensions of the trailer. A standardtrailer has internal dimensions of roughly 53 feet long, but only 8 feetwide and 9 feet tall. When dealing with ultrasonic signals in a closedspace with primarily metal walls, reflections will be numerous. Theplacement of the sensors, as well as the processing of return signalsmust be sufficiently sensitive to detect the presence of cargo in thetrailer, but immune to the false returns generated by reflections of thewalls, floor and ceiling. There exists a need for a cost effectivesystem for detecting the presence of cargo anywhere within a standard 53foot trailer.

[0006] The cargo detector of the present invention includes at least oneultrasonic transducer for covering the entire area of the trailer todetect the presence of an object, especially the area near the ends ofthe trailer. In particular the cargo detector includes short range, longrange, and proximity range modes.

[0007] According to one aspect of the present invention, a cargo trailerdetector consists of a sensor mounted along one wall of the trailer, atrailer tracking control unit connected to the sensor, and a powersource electrically connected to the sensor. The sensor includes a pairof ultrasonic transducers that have multiple operation modes withdifferent ranges. The control unit controls the sensor and receives datafrom the sensor.

[0008] The long range operation mode scans the area adjacent a distalend of the cargo trailer. The area scanned y the long range mode mayextend from 10 to 63 feet and may cover the loading door wall of thecargo trailer.

[0009] The cargo detector may also include an amplifier for amplifyingsignal of one or more ultrasonic transducers to make up for atmosphericabsorption due to sensed atmospheric conditions. Such conditions may betemperature air and/or humidity.

[0010] The area scanned by the short range mode of the cargo sensor,nearer to the sensor itself, may extend from 4 to 20 feet and mayinclude the floor of the cargo trailer.

[0011] Scanning in the proximity mode may be performed continuously todetect presence of any objects in the area from 0 to 4 feet from thesensor. The same transducer as used for the short range mode may also beused for the proximity mode, operating in the proximity mode betweenperiodic short range mode scans. The transducer may be operating inlower power mode when in the proximity mode, as compared to that when inthe short range mode.

[0012] The sensor may be programmed to determine presence or absence ofobjects in the cargo trailer and that information may be transmitted toa central location using a communications control unit connected to thetrailer tracking control unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

[0014]FIG. 1 illustrates a nose mounted cargo detector unit known in theprior art;

[0015]FIG. 2 illustrates a single roof-mounted unit used in the priorart;

[0016]FIG. 3 illustrates multiple ceiling-mounted sensors used in theprior art;

[0017]FIG. 4 illustrates a cargo detector and its interface to acontroller according to the invention;

[0018]FIG. 5 illustrates range of a nose-mounted cargo detectoraccording to one embodiment of the invention;

[0019]FIG. 6 is a front view of the nose-mounted cargo detectoraccording to one embodiment of the present invention;

[0020]FIG. 7 is a circuit diagram illustrating atmospheric sensors;

[0021]FIG. 8 is a circuit diagram illustrating a gain compensationmodule;

[0022]FIG. 9 is a cross-sectional side view of the nose-mounted cargodetector according to one embodiment of the invention;

[0023]FIG. 10 is a flow chart illustrating how atmospheric conditionsare used to adjust sensor gain;

[0024]FIG. 11 is a timing diagram for taking distance measurements.

DETAILED DESCRIPTION OF THE INVENTION

[0025] A description of preferred embodiments of the invention follows.

[0026]FIG. 1 illustrates an ultrasonic sensor detection unit 106 mountedat the nose end 108 of the trailer 102, as is known in the prior art.Although mounting the sensor detection unit at the nose 108 is veryeffective for scenarios when the load is present in the nose of thetrailer, this approach is largely ineffective for detecting the presenceof cargo beyond about 10-20 feet from the nose, as illustrated by range104 of the sensor unit 106.

[0027] The nose-mounted units perform well for the short distances thatthey cover. The primary disadvantage of the nose-mounted units is thatonly a small portion of the cargo space is being examined. Dependingupon weight distribution, a small load may be positioned anywhere in thetrailer space, and thus may be not detectable using a nose-mountedsensor unit 106. Trailer operating companies may be dissatisfied with acargo detection sensor that only samples the nose end of the trailer.

[0028] As illustrated in FIG. 2, in other prior art approaches, thedetector 206 may also be mounted on the ceiling 208 of the trailer. Thispositioning has the advantage of having an easily discernible reflectionback from the floor when the trailer is empty. The positive response ofan empty trailer is useful because it has a definitive signature that ismore easily distinguished from a loaded trailer. However, the ceiling208 is not a prime installation location for trailers. The ceiling of atrailer typically has only one wall. Generally, it is not practical orallowed to have holes in the surface of the ceiling. The cablingrequired for power and the interface may become cumbersome, which alsoadds to installation time and cost. Furthermore, the range 204 of theceiling-mounted detector 206 also may cover only a small portion of theavailable trailer space.

[0029]FIG. 3 illustrates another prior art detection system where cargosensors 206 are located down the length of the trailer. This approachrealizes extremely robust performance for cargo detection. Each unit isonly responsible for detecting objects within 9 feet of its location,which keeps the detection logic very simple. But the cost associatedwith a multiple unit approach such as this is also very high. Inaddition, installation of these units and the cabling that must be runfrom each unit to the host hardware is cumbersome.

[0030] According to one embodiment of the present invention, a singlenose-mounted cargo detector is used to monitor the whole trailer. Thecargo detector may use three different detection modes to cover threedifferent ranges within the cargo compartment.

[0031] As illustrated in FIG. 4, the cargo detector (also called asensor) 406 may be controlled by a communications controller 402, whichmay be in communication with a central system using a wireless network.The communications controller 402 may be employed to receive commandsfor testing and/or modifying settings on the cargo detector 406 and fortransmitting information from the sensor to the central office. Thecommunications controller 402 may be connected to the sensor 406 using awired or wireless connection.

[0032] As will be described in greater detail below, a single controlline may be utilized to switch the cargo detector on for the duration ofeach measurement period. In this way, the cargo detectors samplingperiod is controlled by the host application.

[0033]FIG. 5 illustrates the range modes of a nose-mounted cargodetector 406 according to one embodiment the present invention.

[0034] The cargo detector 406 is configurable for a variety of cargocontainers. For example, the cargo detector may be designed to bemounted at the nose end of the trailer, mounted about 7′ above the floorand centered between the two side walls.

[0035] The cargo detector uses multiple ultrasonic transducers to detectthe presence of objects within its detection path. In a preferredembodiment, the cargo detector has three modes of operations, whereineach mode is responsible for detection objects in a different spacewithin the trailer. The three modes are:

[0036] Short Range Mode

[0037] Long Range Mode

[0038] Proximity Mode

[0039] The three modes are each optimized for a specific detectionrange. The combination of these three modes makes the detector effectiveacross the entire 53′ of a trailer.

[0040] The short range mode is designed to handle the condition when aload is placed at the nose of the trailer. It is effective for loads inthe short range 510 of 4′ to 20′. For this mode, a pair of 40 kHztransducers, one for transmit and one for receiver, may be used. Thetransducers are pointed downward toward the floor of the trailer. Forthis mode, the return response of the floor is known and expected for anempty trailer. A return that is significantly different is determined tobe due to cargo. The cargo detector returns the distance to the objectas its measurement. The short range sensors may be arranged so as tosweep the whole floor area from one side wall to another.

[0041] A long range mode is designed to handle the condition when a loadis placed anywhere down the length of the trailer. It is effective forloads in the range 508 of 10′ to 63′. For this mode, a pair (receive andtransmit) of 25 kHz transducers is used. The transducers are angled downslightly to traverse the entire length of the trailer, so that energyreacts the back door 512 area. The transducers are preferably mounted atthe base of parabolic cones within the unit 406, to focus the ultrasonicenergy and extend their range. Furthermore, to ensure accuracy down thelength of a 53′ trailer across all environmental conditions, the longrange mode utilizes readings of the air temperature and humidity tocompensate for the attenuation and propagation properties of the air atthe time of the measurement. Compensating for atmospheric absorption isdiscussed further in connection with FIGS. 9-12.

[0042] The cargo detector returns the distance to the object as itsmeasurement. In that the cargo detector routinely detects the back wall512 of the trailer, the length of the trailer is known to the hostapplication to discriminate between a load and an empty trailer. Thisdiscrimination may be accomplished, for example, by collecting numeroustest samples of what a reflection from an empty trailer looks like and acomparative reflection for a trailer containing cargo. The sensorelectronics may then be configured to make a determination of whetherany objects are located in the trailer based on the learned knowledgeabout different reflective patterns.

[0043] The third, proximity mode is designed to handle the conditionwhen a load is placed within a few feet of the sensor, or even flushagainst the nosewall. This is a critical mode of the cargo detector, inthat a load placed against the detector will dampen any pings and defeatthe distance measuring modes of the short range and long range sensors.It is effective from 0″ (object placed flush against cargo detector) to4′. In this mode, the 40 kHz transducers are utilized in a low powermode, but allowed to run continuously. The presence of a return signalindicates that there is an object within its range. In this case, thedetector returns the magnitude of the return signal as its measurement.

[0044] The control unit (see FIG. 7) contains a microcontroller andassociated circuitry that powers up the cargo detector on apredetermined schedule, and commands a collection of measurements usingthe three modes identified above. The detectors return the threemeasurement values, and the control unit uses those measurements to makean assessment as to whether the container space is loaded or empty. Forthe control unit application, there is additional filtering that is donein the logic to ensure a load change has occurred.

[0045] Because any detection algorithm can yield marginal results, thecargo detector is designed to perform its measurements using one of twodifferent sets of thresholds. With conventional cargo detection, a loadthat is marginally detectable may yield inconsistent measurementresults. This can cause the sensor to oscillate between loaded and emptyuntil the load status changes.

[0046] By utilizing two sets of thresholds, the control unit can tellthe cargo detector which set of thresholds to use based on the currentassessment of whether the trailer is loaded or empty. This provides aguard band between loaded and empty that must be crossed to reverse theexisting measured state. This adds considerable reliability to the loaddetermination.

[0047] With the basic design as discussed in this disclosure, the cargodetector achieves better than 98% detection accuracy of load and emptyevents.

[0048]FIG. 6 shows a front view of the cargo detector 406 assemblyaccording to one embodiment of the present invention. As discussedabove, the cargo detector 406 has at least two pairs of ultrasonictransducers, short range 610 a and 610 b, and long range 604 a and 604b, each consisting of an ultrasonic transmitter and a detector. The longrange transmitter and detector 604 a-b are mounted within elliptic cones602 a-b to improve the efficiency of the sensor.

[0049] The atmospheric conditions inside the trailer may affect theaccuracy of the measurements because they may change the amount ofabsorption of the ultrasonic signal. For example, humidity of thetemperature may affect absorption of the ultrasonic signal, while thetemperature of the air may affect propagation time of the signal, whichmay also have effect on the distance measurements that are used todetermine whether there is an object present in the cargo trailer. Thelong-range sensor signal may be adjusted and amplified in order tocompensate for the atmospheric conditions. There are holes 612 a-b inthe face plate of the sensor 406 to promote airflow through the case insuch a way as to draw the air across the temperature and humiditysensors. The temperature and humidity sensors are used to judge theatmospheric absorption.

[0050] The short range transmitter and detector 610 a-b do not need tobe mounted within cones because the range of their operation is limitedcompared to the long range transducer. In an alternative embodiment ofthe invention, the short-range transducer may likewise be mounted withinthe elliptic cone to improve power efficiency.

[0051] In one embodiment of the invention, the short range transducers610 a-b are mounted facing the floor of the trailer. In an alternativeembodiment of the invention, the angle of mounting of the short-rangeultrasonic transducer may be varied based on the height at which thesensor is positioned.

[0052] The short range transducer may also be employed to operate in theproximity mode to provide cargo detection within the short rangedistances. The sensor controller may set the short range transducer tooperate at lower power levels when it is in the proximity mode. Theproximity mode detection may be performed continuously, while theshort-range detection may be performed periodically at predeterminedtime intervals. The low gain proximity mode operates by simultaneouslytransmitting and receiving signals and determining if reflection ispresent.

[0053] The cargo detector may be mounted between the inside and outsidewalls of the nose end of the trailer, such that the front panel 640 ofthe sensor 406 is flush with the inside wall of the trailer. In analternative embodiment of the invention, a different mounting positionmay be used, as determined by one skilled in the art.

[0054] The cargo detection module 406 may be controlled by controlcircuit 902 (see FIG. 7). A microprocessor (microcontroller) 702 is themain component of the control circuit 902, and connected to it arehumidity and temperature sensors 706 and 704, correspondingly, andvarious other amplifier and power components.

[0055] Illustrated in FIG. 8 is the electronics for gain compensationfor the atmospheric absorption. The transducer signal of interest isselected from the input signal 802 using a series of Field EffectTransistors (FETs). The signal passes through three stages of fixed gainamplification before going through a fourth, variable-gain stage. Thepotentiometer is used to set the resistor divider on the feedback pathon the fourth stage, which allows for setting the gain of the fourthstage in the range between 6 db and 44 db.

[0056] The cargo sensor may be operated in one of the following modes:measurement mode, testing mode, and reprogram mode. In the measurementmode, the sensor sequences through all possible measurements and thenprovides a short binary packet with the results of all of themeasurements. This packet may then be sent to the controller 402.

[0057] In the terminal mode, the sensor provides a menu interface, usingwhich a user can program the sensor for individual tests orcomprehensive measurement sequences. This interface may be run, forexample, on a terminal-based host, such as a computer runningHyperTerminal.

[0058] In the reprogram mode, the startup code erases and reprograms theruntime segment of the sensor controller based on a byte stream receivedfrom the communication interface. Such byte stream may be sent, forexample, from the central office using the controller 402, or from thecontroller 402 directly.

[0059]FIG. 9 is a side view of the cargo sensor according to oneembodiment of the invention. As illustrated, between the back panel 904and the front panel 614, there is a sensor controller 902 connected totransducers 610 and 604. A long range transducer 604 is mounted withinan elliptical cone 602, and short range transducer 610 is mounted at adownward angle, pointing towards the floor. The openings 612 a-bfacilitate the air flow within the sensor, so that air temperature andhumidity may be more accurately measured.

[0060]FIG. 10 is a flow chart illustrating operation of the atmosphericabsorption compensation module. The atmospheric absorption compensationmodule determines the signal amplification necessary to compensate forthe air conditions based on a set of measurements provided by varioussensors.

[0061] The ambient temperature is measured in step 1004 by taking areading of the temperature sensor 704. The temperature is critical inthat it is a significant factor in the speed of sound which, in turn,affects the sensors ability to measure distance to the back wall of thetrailer.

[0062] The distance is measured in step 1006 using a distance timer. Thedistance timer is an interrupt set to a rate that corresponds to theamount of time (based on speed of the sound) for a signal to travel andreturn through a predetermined distance, for example, through ½ foot.FIG. 11 is a timing diagram for distance measurement. The interrupt isused to determine the distance that the sound has traveled whenevaluating return response.

[0063] The relative humidity of the air may be determined in step 1008by sampling the analog voltage across the humidity sensor 706. Thereceived may then be adjusted for accuracy over temperature.

[0064] In general, the atmospheric absorption is affected by airtemperature, humidity and the frequency of the signal. Additionalfactors such as, for example, the atmospheric pressure, may also affectthe atmospheric absorption, and in an alternative embodiment of theinvention, additional sensors may be employed to sense those factors.

[0065] The signal loss due to atmospheric conditions is calculated instep 1010. In order to calculate the signal loss factor, pre-calculatedtables may be employed. For example, two-dimensional tables may specifythe amount of signal loss per half a foot for specific values oftemperature and relative humidity. There may be different tables fordifferent frequencies, for example, one table for the long range sensing(25 kHz), and another one for the short range sensing (40 kHz). A2-dimensional interpolation between the table values may be performed todetermine the expected signal loss for the measured environmentalconditions.

[0066] In step 1012, the loss factor is accumulated at the distancetimer rate to determine the amount of gain necessary for the returnedsignal. The transmitted signal may then be amplified based on thecalculated necessary gain.

[0067] While this invention has been particularly shown and describedwith references to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. An apparatus for detecting an object in a cargotrailer comprising: a sensor mounted along a first wall of the trailer,the sensor having a pair of ultrasonic transducers having multipleoperation modes with different ranges, with at least one operation modescanning an area of the cargo trailer adjacent a distal end of thetrailer from the first wall on which the sensor is mounted; a trailertracking control unit connected to the sensor, the control unitcontrolling the sensor and receiving data from the sensor; and a powersource electrically connected to the sensor.
 2. The apparatus of claim1, wherein the multiple operation modes include short range mode, longrange mode, and proximity mode.
 3. The apparatus of claim 2, whereinarea scanned by the long range mode extends from 10 to 63 feet.
 4. Theapparatus of claim 2, wherein area scanned by the long range modeincludes a loading door wall of the cargo trailer.
 5. The apparatus ofclaim 4, further comprising an amplifier for amplifying signal of atleast of the ultrasonic transducers to make up for atmosphericabsorption.
 6. The apparatus of claim 5, further comprising at least onesensor sensing an atmospheric condition.
 7. The apparatus of claim 6,wherein the atmospheric condition is at least one of air temperature andair humidity.
 8. The apparatus of claim 2, wherein area scanned by theshort range mode includes a floor of the cargo trailer.
 9. The apparatusof claim 2, wherein area scanned by the short range mode extends from 4to 20 feet.
 10. The apparatus of claim 2, wherein scanning is performedcontinuously in the proximity mode.
 11. The apparatus of claim 10,wherein area scanned by the proximity mode extends from 0 to 4 feet. 12.The apparatus of claim 2, wherein one transducer is used for the shortrange mode and for the proximity mode.
 13. The apparatus of claim 12,wherein the one transducer operates periodically when operating in theshort range mode.
 14. The apparatus of claim 13, wherein the onetransducer operates continuously in the proximity mode when notoperating in the short range mode.
 15. The apparatus of claim 12,further comprising control electronics for lowering output power of theone transducer when it operates in the proximity mode.
 16. The apparatusof claim 1, further comprising a control unit adapted to communicatewith a central system.
 17. The apparatus of claim 16, wherein thecontrol unit uses signals detected in the multiple operation modes todetect presence or absence of cargo in the cargo trailer.
 18. Theapparatus of claim 1, wherein the sensor is mounted flush with a nosewall of the trailer.
 19. The apparatus of claim 1, wherein at least oneultrasonic transducer is a long range transducer which comprises anultrasonic transmitter and an ultrasonic receiver.
 20. The apparatus ofclaim 19, wherein the transmitter and the receiver are mounted at thebase of a pair of parabolic cones.
 21. The apparatus of claim 1, whereinat least one ultrasonic transducer is a short range mode transducerwhich comprises an ultrasonic transmitter and an ultrasonic receiver.22. The apparatus of claim 21, wherein the transmitter and receiver aremounted pointing downward towards floor of the trailer.
 23. An apparatusfor detecting an object in a trailer comprising: a long-range sensormounted along a nose wall of the trailer; an atmospheric absorptioncompensation module connected to the sensor; and a power sourceelectrically connected to the sensor.
 24. The apparatus of claim 23,wherein the atmospheric absorption compensation module further comprisesat least one sensor sensing an atmospheric condition.
 25. The apparatusof claim 24, wherein the atmospheric condition is at least one of airtemperature and air humidity.
 26. The apparatus of claim 23, wherein theatmospheric absorption compensation module further comprises controlsfor amplifying sensor signal.
 27. The apparatus of claim 23, wherein theatmospheric absorption compensation module further comprises a processorfor calculating effects of atmospheric absorption on ultrasonic signal.28. An apparatus for detecting an object in a cargo trailer comprising:a sensor mounted along a first wall of the cargo trailer, the sensorcomprising a first ultrasonic transducer operating in a long range modethat scans out to an area adjacent a second wall, of the trailer, therear wall being opposite and distal of the first wall, and a secondultrasonic transducer adapted to operate in a short range mode and in aproximity mode; a control module for controlling operation of thesensor; and a power source electrically connected to the sensor and thecontrol module.
 29. The apparatus of claim 28, wherein range of areascanned in the proximity mode is from 0 to 4 feet.
 30. The apparatus ofclaim 28, wherein the second ultrasonic transducer operates at lowerpower when operating in the proximity mode.
 31. The apparatus of claim28, wherein the second ultrasonic transducer operates in the short rangemode periodically.
 32. The apparatus of claim 31, wherein the secondultrasonic transducer continuously operates in the proximity mode whennot operating in the short range mode.